The present invention relates to a reversible optoelectronic device for use in a narrow range of light wavelength, comprising at least one transparent surface region of a first conductivity type and an assembly of two active regions, of which one active region has a first conductivity type and another active region is of the opposite type. The active regions determined a semiconductor junction having electroluminescent and photosensitive properties, the material of the assembly of the two active regions having a smaller forbidden bandwidth than that of the material of the surface region.
In telecommunications, coupling circuits require semiconductor components, in particular radiation emitters such as electroluminescent diodes and lasers, receivers, such as photodiodes, and transmission means which are usually optical fibers. In certain cases, the telecommunications are in two senses; for example, in telephony it appears advantageous transmission-type systems to use components which can also be used readily in emitters and in receivers.
The transmission-type systems preferably use determined light wavelengths that correspond with those providing the best; transmission efficacies by optical fibers, in particular, the narrow bands of the spectrum centered on 1.06 .mu.m and on 0.83 .mu.m, the electroluminescent source devices for which contain an active part where a p-n junction is situated and a transparent surface layer made from a material having a forbidden bandwidth larger than that of the material of the active part.
However, these known devices, if they have good characteristics in electroluminescence, are not good photo-receivers; the conditions of optimizing their characteristics and those of a photosensitive diode are considered different, even opposite, in particular as regards the doping levels, the depth of the junction or the levels of polarisation voltage. For example, the efficacy of the electroluminescent diode increases with the doping level; on the contrary, a photodiode is preferably little doped in order that its capacity be minimum, such capacity determining actually the rapidity of the response of the diode. In the same way, the junction of the electroluminescent devices is sufficiently deep, so that the recombinations near one surface are not radiative. On the contrary, a large depth is a drawback in the case of photodetection, for it entails a stronger absorption outside the collecting region of carriers.
In electroluminescent devices it is endeavoured to eliminate the absorption of the emitted radiation, which absorption is on the contrary necessary in the active part of a photodiode. It is to be noted that the absorption is defined here by the coefficient of absorption .alpha. of a material, or by the absorption length L which is the distance at which the intensity of a radiation is reduced in a ratio (1/e), .alpha. being equal to 1/L.